This invention relates to a method for generating and adjusting a predetermined quantity of mutually independent direct current voltages by converting corresponding digital values stored in read-write memory (RAM) using a digital-to-analog converter (DAC). The invention also relates to a system for practicing the method. More particularly, the invention refers to the use of the method and system in an ultrasonic test instrument of the kind used for ultrasonic nondestructive testing of materials.
For the purpose of adjusting electronic equipment or adapting such equipment to different operating conditions it is often necessary to provide d.c. voltages which remain constant during a given measurement period but can then be adjusted very rapidly. Direct current voltages of this kind are required, for example, for setting evaluation threshold levels of an amplitude gate, for changing gate times, and for indicating pulse signal peaks on a display screen of an ultrasonic test instrument.
The general practice is to generate these adjustable d.c. voltages by means of potentiometer circuits. The potentiometer circuit has the disadvantage of requiring each d.c. voltage to be produced by a separate potentiometer on the front or control panel of the equipment. In such cases, apart from the considerable amount of space required, manual adjustment of the equipment is complicated and errors can occur very easily in operation.
In radio and television technology it is known to generate a plurality of mutually independent d.c. voltages using, for example, just one potentiometer or other means, to convert the d.c. voltages to digital values by means of an analog-to-digital converter (ADC) and store the values in digital memories so that they will be available as d.c. voltages upon recall and digital-to-analog conversion. These known devices are designed specifically to provide d.c. voltages to control voltage-variable capacitors for tuning the equipment to a predetermined reception freqency (see, for example, German Offenlegungsschrift No. 25 20 676). Since these d.c. voltages are generated simultaneously, a disadvantage of the equipment is that a separate DAC is required for each d.c. voltage to be set. Another disadvantage is that the d.c. voltages to be stored initially have to be produced by means of at least one potentiometer or an up/down counter, and the voltage has to be produced anew for each change of value. Under such conditions it is imposible or too cumbersome to obtain a permanent and rapidly adjustable arrangement for the d.c. voltages, because the d.c. voltages have to be preset by means of a control element.